Hey all, As the title suggests, I've found some recurring structure on an SEM image and I can't for the life of me figure out what it is. I took the image this morning. Here she is: http://i.imgur.com/nFuBsW2.png Here's a larger, more zoomed out and higher res version. A few more of the mystery objects are visible. http://i.imgur.com/gEXW4KN.jpg I found plenty of these things. Here's some background on the sample. This was a piece of pyrex from a glass cell that contained a mixture of xenon and nitrogen gas. It also contained rubidium. The cell was continuously irradiated with 795 nm laser light, and heated sometimes up to 180 C. We washed out the rubidium by slowly reacting it with alcohol before breaking the cell open. I've been examining the cell surface looking for etching or pitting in the glass possibly caused by xenon excimers. So far, inconclusive. But I've been completely baffled by these circular structures that keep appearing. They were not present at all on a control piece of pyrex that I imaged. Does anyone recognize this? What might it be? Thanks!